Injection molding machine

ABSTRACT

An injection molding machine according to the invention includes a motor, a driver circuit that drives the motor; and a rectifying part that supplies electric power to the driver circuit. A regenerative line for regenerative electric power of the motor is connected to the rectifying part in parallel. A converting part and a harmonics component reducing part are provided in the regenerative line. The converting part converts direct electric power between the driver circuit and the rectifying part into alternating electric power which is input to the harmonics component reducing part.

FIELD

The present invention is related to an injection molding machine which includes a motor, a driver circuit that drives the motor; and a rectifying part that supplies electric power to the driver circuit.

BACKGROUND

Japanese Laid-open Patent Publication No. 2006-54947 discloses a converter which performs regeneration to a power supply when a voltage across a DC link exceeds a predetermined upper limit voltage.

However, according to Japanese Laid-open Patent Publication No. 2006-54947, powering electric power and regenerative electric power are generated via the same A/C converter circuit, and thus the regenerative electric power generated at the time of decelerating the motor can not regenerated effectively.

SUMMARY

An injection molding machine according to an embodiment includes a motor, a driver circuit that drives the motor; and a rectifying part that supplies electric power to the driver circuit. A regenerative line for regenerative electric power of the motor is connected to the rectifying part in parallel. A converting part and a harmonics component reducing part are provided in the regenerative line. The converting part converts direct electric power between the driver circuit and the rectifying part into alternating electric power which is input to the harmonics component reducing part.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for illustrating a configuration of an injection molding machine according an embodiment of the present invention.

FIG. 2 is a diagram for schematically illustrating an example of a motor driving power supply circuit including a converter of the injection molding machine.

FIG. 3 is a diagram for illustrating an example of a circuit configuration of the converter.

FIG. 4 is a diagram for illustrating a first configuration example of a harmonics component reducing part.

FIG. 5 is a diagram for illustrating a second configuration example of a harmonics component reducing part.

FIG. 6 is a functional block diagram of a controller 26.

FIG. 7 is a flowchart for illustrating a method of controlling the converter according to the present embodiment.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments for carrying out the present invention will be described in detail by referring to the accompanying drawings. FIG. 1 is a diagram for illustrating a configuration of an injection molding machine 1 according an embodiment of the present invention.

The injection molding machine 1, which is a motor-operated injection molding machine in the illustrated example, includes a servo motor for injection 11. The rotation of the servo motor for injection 11 is transmitted to a ball screw 12. A nut 13, which is moved in the forward and backward directions by the rotation of the ball screw 12, is fixed to a pressure plate 14. The pressure plate 14 is configured to be movable along guide bars 15 and 16 which are fixed to a base frame (not illustrated). The motion of the pressure plate 14 in forward and backward directions is transmitted to a screw 20 via a bearing 17, a load cell 18 and an injection shaft 19. The screw 20 is disposed in a heating cylinder in such a manner that it can rotate in the heating cylinder 21 and can move in an axial direction. A hopper 22 for supplying a resin is provided in a rear portion in the heating cylinder 21. The rotational motion of a servo motor for screw rotation 24 is transmitted to the injection shaft 19 via coupling members 23 such as a belt, a pulley, etc. In other words, the screw 20 is rotated when the injection shaft 19 is driven to rotate by the servo motor for screw rotation 24.

In a plasticizing/metering process, the screw 20 is rotated and moved backward in the heating cylinder 21, thereby molten resin is stored in a front portion of the screw 20, that is to say, on the side of a nozzle 21-1 of the heating cylinder 21. In an injecting process, molds (dies) are filled with the molten resin stored in the front portion of the screw 20, and molding is performed by applying pressure. At that time, a force pressing the resin is detected by the load cell 18 as a reaction force. In other words, a resin pressure in the front portion of the screw 20 is detected. The signal representing the detected pressure is amplified by a load cell amplifier 25 and input to a controller 26 (a control apparatus) functioning as controlling means. Further, in a holding process, the pressure of the resin filling in the molds is held at a predetermined pressure.

A position detector 27 for detecting an amount of movement of the screw 20 is attached to the pressure plate 14. The detection signal of the position detector 27 is amplified by an amplifier 28 and input to the controller 26. This detection signal may be used to detect a movement speed of the screw 20.

The servo motor 11 and 24 are provided with encoders 31 and 32 for detecting a number of revolutions, respectively. The numbers of revolutions detected by the encoders 31 and 32 are input to the controller 26.

A servo motor 42 is provided for opening and closing the molds, and a servo motor 44 is provided for extruding (ejecting) a molded article. The servo motor 42 drives a toggle link (not illustrated), for example, to implement the mold opening/closing. Further, the servo motor 44 moves an ejector rod (not illustrated) via a ball screw mechanism, for example, to implement the ejection of the molded article. The servo motor 42 and 44 are provided with encoders 43 and 45 for detecting a number of revolutions, respectively. The number of revolutions detected by the encoders 43 and 45 are input to the controller 26.

The controller 26 is comprised mainly of a microprocessor that includes a CPU, a ROM in which control programs are stored, a RAM in which calculation results are stored, a timer, a counter, an input interface, an output interface, etc., for example.

The controller 26 transmits current (torque) instructions to motor driver circuits according to the respective processes in an injection molding process. The motor driver circuits drive the servo motors 11, 24, 42 and 44 used in the respective processes according to the instructions. For example, the controller 26 controls the number of revolutions of the servo motor 24 with the motor driver circuit 52 to implement the plasticizing/metering process. Further, the controller 26 controls the number of revolutions of the servo motor 11 with the motor driver circuit 51 to implement the injecting process and the holding process. Further, the controller 26 controls the number of revolutions of the servo motor 42 with the motor driver circuit 53 to implement the mold opening process and the mold closing process. Further, the controller 26 controls the number of revolutions of the servo motor 44 with the motor driver circuit 54 to implement the molded article ejecting process.

A user interface 35 includes an input setting part with which injection molding conditions can be set for the respective processes, such as a mold opening/closing process, an injecting process, etc. Further, the user interface 35 includes an input part with which a user inputs various instructions and an output part (a display part, for example) configured to output various items of information.

Typically, a cycle of the injection molding process in the injection molding machine 1 includes a mold closing process for closing the molds; a mold clamping process for clamping the molds; a nozzle contacting process for abutting a nozzle 21-1 onto a sprue (not illustrated) of the molds; an injecting process for moving the screw 20 in the heating cylinder 21 to inject the molten resin stored in the front portion of the screw 20 into a mold cavity (not illustrated); a holding process for maintaining the dwell pressure afterward for a while so as to prevent emergence of air bubbles and sink marks; a plasticizing/metering process and a cooling process for melting the resin and storing the molten resin in the front portion of the heating cylinder 21 by rotating the screw 20 so as to prepare for the next cycle, utilizing the time until the molten resin filling in the mold cavity is cooled to set; a mold opening process for opening the molds; and a molded article ejecting process for pushing the molded article out with ejector pins (not illustrated) provided in the mold.

FIG. 2 is a diagram for schematically illustrating an example of a motor driving power supply circuit including a converter 100 of the injection molding machine 1. In FIG. 2, the servo motor for injection 11 and a motor driver circuit 51 for driving the servo motor for injection 11 are illustrated as an example. Other servo motors 24, 42 and 44 and the motor driver circuits 52, 53 and may be the same. According to an alternative embodiment, the converter 100 may be connected to servo motors and motor driver circuits for driving the servo motors in parallel.

The converter 100 is connected to a power supply 200. The power supply 200 may be an AC power supply. Further, the converter 100 is connected to the servo motor 11 via a DC link 300 and the motor driver circuit 51. The converter 100 converts the electric power from the power supply 200 to supply the converted electric power to the servo motor 11 via the DC link 300 and the motor driver circuit 51. The motor driver circuit 51 may be an inverter for converting the output (direct electric power) of the converter 100 to a three-phase alternating electric power, for example, and the inverter may include a three-phase bridge circuit having six power transistors, for example. The DC link 300 includes a capacitor (a capacitor), a bus bar, a cable, or the like.

A voltage detecting part 190 is provided such that it detects a voltage across the DC link 300 which is provided between the output side of a rectifier 102 (see FIG. 3) and the input side of the motor driver circuit 51. A direct voltage detected by the voltage detecting part 190 is supplied to the controller 26 (see FIGS. 3 and 6).

FIG. 3 is a diagram for illustrating an example of a circuit configuration of the converter 100. In the example illustrated in FIG. 3, the converter 100 includes terminals R, S and T which are connected to the AC power supply and terminals P and N which are connected to the DC link 300. The converter 100 includes the rectifier (powering circuit part) 102 which is formed of a three-phase diode bridge including six diodes, and a bridge circuit (regenerating circuit part) 104 which is formed of a three-phase inverter including six transistors. It is noted that in FIG. 3 a flow of the electric power at the time of a powering mode and a flow of the electric power at the time of a regenerating mode are indicated by arrows.

The rectifier 102 performs a conversion operation (powering operation) from the alternating electric power to the direct electric power in the DC link 300 with diode rectification. The bridge circuit 104 performs a PWM (Pulse Width Modulation) control according to a driving signal output from a PWM generator 71 to implement a conversion operation (power supply regenerating operation) from the direct electric power in the DC link 300 to the alternating electric power in the alternating power supply. The bridge circuit 104 controls magnitude of the alternating electric power (alternating electric current) between the alternating power supply and the bridge circuit 104 and magnitude of the direct electric power (direct electric current) of the DC link 300 during the power supply regenerating operation.

As illustrated in FIG. 3, the converter 100 includes a regenerative line 82 connected to a powering line 81 in parallel. The powering line 81 is between the alternating power supply and the motor driver circuit and has the rectifier 102 provided therein. The regenerative line 82 is connected to the input and the output of the rectifier 102 in parallel. One end of the regenerative line 82 is connected to an alternating current line part of the powering line 81 on the input side of the rectifier 102, and another end of the regenerative line 82 is connected to a direct current line part of the powering line 81 on the output side of the rectifier 102. The regenerative line 82 has the bridge circuit 104 and a harmonics component reducing part 63 inserted in series therein.

The bridge circuit 104 is a converting part which converts the direct electric power between the output side of the rectifier 102 and the input side of the motor driver circuit 51 (see FIG. 2) into the alternating electric power. The alternating electric power output by the power conversion operation of the bridge circuit 104 is input to the harmonics component reducing part 63. The harmonics component reducing part 63 may function as a low-pass filter.

The harmonics component reducing part 63 includes plural inductors inserted to the respective phases of R, S and T in series and capacitors (capacitors) connected between the inductors, for example. The harmonics component reducing part 63 may have a Y-connection configuration in which plural capacitors whose ends are connected to the respective phases are commonly connected at a neutral point, as illustrated in FIG. 4. The harmonics component reducing part 63 may have a delta connection configuration in which the capacitors are connected between the respective phases, as illustrated in FIG. 5. Further, the harmonics component reducing part 63 may be configured such that only the inductors are inserted to the respective phases in series.

Further, the injection molding machine 1 includes, as a controlling part of the converter 100, the controller 26, the PWM generator 71 which generates a PWM driving signal, and a phase detecting part 72 which detects a phase of the alternating voltage in a line connecting between the output side of the harmonics component reducing part 63, the alternating power supply and the input side of the rectifier 102. The controller 26 performs the PWM control of the bridge circuit 104 with the PWM generator 71 to regenerate the electric power of the servo motor 11 which is input to the bridge circuit 104 via the motor driver circuit 51.

The controller 26 controls the regenerating operation of the bridge circuit 104 with the PWM driving signal generated by the PMW generator 71 such that the alternating current output from the bridge circuit 104 is shaped to have a shape of a sine wave. The PWM control has advantage over the non-PWM control in that it can reduce the harmonics current, which is generated by the switching operations of the transistors of the bridge circuit 104 and passes to the alternating power supply, and improve the power-factor at the time of regenerating.

The controller 26 controls the regenerating operation by the power converting operation of the bridge circuit 104 with the PMW generator 71, based on a direct voltage value Vdc detected by the voltage detecting part 190 (see FIG. 2), an alternating current value Iacf detected by a current detecting part 61 between the alternating output side of the bridge circuit 104 and the alternating input side of the harmonics component reducing part 63, and an alternating voltage value Vacf detected by a voltage detecting part 62, such that the alternating current output from the bridge circuit 104 has a sine wave shape with a target frequency. A phase detecting part 72 is capable of detecting the phase of the alternating voltage based on the alternating voltage value Vacf detected by the voltage detecting part 62.

For example, the controller 26 generates an instruction value Ir of the alternating current by performing processes, such as a process of multiplying a voltage error output Verr, which is generated according to an error between an instruction value Vr of the direct voltage and the direct voltage value Vdc supplied from the voltage detecting part 190, by the alternating voltage value Vacf supplied from the phase detecting part 72. Then, the controller 26 supplies an current error output Ierr, which is generated according to an error between the instruction value Ir and the alternating current value Iacf supplied from the current detecting part 61, to the PMW generator 71. The PMW generator 71 compares the current error output Ierr with a predetermined carrier such as a triangle wave to generate the PWM driving signal for driving the gates of the transistors of the bridge circuit 104 to implement the regenerating operation.

FIG. 6 is a functional block diagram of the controller 26 which functions as a control apparatus of the converter 100. It is noted that the control apparatus of the converter 100 may be implemented by a control apparatus other than the controller 26.

The controller 26 includes a converter controlling part 261 and a regeneration determining part 263. The controller 26 includes one or more calculation processing apparatuses and a storage device for storing software (programs) and data, etc., such as a RAM and a ROM. The respective functional parts 261 and 263 of the controller 26 are functional parts for performing various processes for input data, using the calculation processing apparatus mainly, and are implemented by a hardware resource, a software resource or a combination thereof. The functions of the respective functional parts 261 and 263 are described with reference to FIG. 7.

FIG. 7 is a flowchart for illustrating an example of a method of controlling the converter 100 according to the present embodiment. The control process illustrated in FIG. 7 is executed by the controller 26 in connection with the regeneration of the servo motor 11 (at the time of decelerating the injection speed in the case of the servo motor 11).

In step 10, the regeneration determining part 263 acquires a voltage Vdc across the capacitor of the DC link 300 with the voltage detecting part 190 to determine the regenerating status of the motor.

In step 12, the regeneration determining part 263 determines whether the voltage Vdc of the DC link 300 is greater than a predetermined threshold voltage Vth. The regeneration determining part 263 determines that the motor is not in the decelerated status, that is to say, the motor does not generate the regenerative electric power if the voltage Vdc is not greater than the predetermined threshold voltage Vth. If it is determined by the regeneration determining part 263 that the voltage Vdc is not greater than a threshold voltage Vth (i.e., it is determined that the motor does not generate the regenerative electric power), the converter controlling part 261 controls the transistors of the bridge circuit 104 such that all the transistors are tuned off, thereby not performing the regenerating operation of the bridge circuit 104. On the other hand, if the voltage Vdc is greater than the predetermined threshold voltage Vth, the regeneration determining part 263 determines that the motor is in the decelerated status, that is to say, the motor generates the regenerative electric power.

In step 14, the converter controlling part 261 starts the regenerating operation, if the voltage Vdc is not greater than the threshold voltage Vth based on the determination result of the regeneration determining part 263. In step 16, the converter controlling part 261 performs the switching operations of the transistors of the bridge circuit 104 with the PWM control such that the alternating current output from the bridge circuit 104 has a shape of a sine wave (step 16).

In steps 16, 18 and 20, the converter controlling part 261 stops the regenerating operation of the bridge circuit 104 by tuning off all the transistors of bridge circuit 104, if it is determined by the regeneration determining part 263 that a regeneration stop criterion is met. For example, the regeneration determining part 263 determines that the regeneration stop criterion is met, if the direct voltage value detected by the voltage detecting part 190 is smaller than a predetermined voltage value which is smaller than the threshold voltage Vth and a peak value of the alternating current detected by the current detecting part 61 is smaller than a predetermined current value.

In this way, according to the embodiment, since the regenerative line 82 is provided in parallel to the powering line 81, the regenerative electric power can be effectively recovered, thereby reducing the energy consumption. Further, since the bridge circuit 104 and the harmonics component reducing part 63 have only the regenerative current passing therethrough (i.e., the powering current does not pass through the bridge circuit 104 and the harmonics component reducing part 63), a rating can be decreased in comparison with a case where a powering line and a regenerative line is common. For example, it is possible to select the switching elements such as the transistors, the inductors, etc., according not to the powering electric power but instead to regenerative electric power. Further, the regeneration by the PWM control using the PMW generator 71 increases the power factor.

The present invention is disclosed with reference to the preferred embodiments. However, it should be understood that the present invention is not limited to the above-described embodiments, and variations and modifications may be made without departing from the scope of the present invention.

For example, according to the present embodiment, a voltage or a current as a dimension of a physical quantity is used for control; however, substantially the same control can be performed by equivalently using other dimensions of a physical quantity such as energy.

The present application is based on Japanese Priority Application No. 2011-163695, filed on Jul. 26, 2011, the entire contents of which are hereby incorporated by reference. 

1. An injection molding machine, comprising: a motor; a driver circuit that drives the motor; a rectifying part that supplies electric power to the driver circuit; a regenerative line of regenerative electric power of the motor connected to the rectifying part in parallel; and a converting part and a harmonics component reducing part provided in the regenerative line, the converting part converting direct electric power between the driver circuit and the rectifying part into alternating electric power which is input to the harmonics component reducing part.
 2. The injection molding machine of claim 1, wherein the converting part operates such that an electric current wave-shape of the converted alternating electric power corresponds to a shape of a sine wave.
 3. The injection molding machine of claim 1, further comprising: a controlling part that controls an operation of the converting part.
 4. The injection molding machine of claim 3, wherein the controlling part controls a regenerative operation of the converting part according to a direct voltage between the driver circuit and the rectifying part.
 5. The injection molding machine of claim 3, wherein the controlling part performs a PWM control of the converting part based on the direct voltage between the driver circuit and the rectifying part, an alternating voltage between the converting part and the harmonics component reducing part, and an alternating voltage at an output side of the harmonics component reducing part. 